Technical Field
The present invention relates to a particle measuring device suitable for measuring particles suspended in a gas such as air (that is, an aerosol).
Background Art
Particle measuring devices in which particles suspended in a gas such as air (that is, an aerosol) are formed into a beam shape and then the resulting flow path is irradiated with laser light to measure the particles are one type of conventional, well-known particle measuring devices used for purposes such as monitoring semiconductor manufacturing environments or measuring particulate contaminates in the atmosphere. In this type of device, the scattered light produced when the laser light hits the particles is detected and used to evaluate the particles, and therefore the intensity of the laser light used to irradiate the particles is one of key factors in achieving high sensitivity. However, due to the principles behind generation of laser light, the intensity of the laser light produced by the laser emitter inevitably decreases to some degree when that light is extracted.
In order to solve this problem, Patent Document 1, for example, discloses a scattered light-type particle detector in which a particle flow path is formed within an external mirror-type laser resonator, and the particles are measured by irradiating them with laser light which has experienced no loss in energy. Moreover, Patent Document 2, for example, discloses a particle detection device in which an optical resonator is provided separately from the laser resonator and used to amplify the energy of the laser light in order to create resonant laser light. A particle flow path is formed within the optical resonator, and the particles are measured by irradiating them with the resonant laser light. Furthermore, Patent Document 3, for example, discloses a particle measuring device that includes an external optical resonator for the same purpose as in Patent Document 2, and the external optical resonator includes a detector that monitors the wavelength of the amplified-energy resonant laser light. The particle measuring device disclosed in Patent Document 3 also includes a mechanism that adjusts the distance between reflective mirrors in the external optical resonator according to the difference between the detected resonant wavelength and the wavelength of the laser emitter.